Gas turbine engines are often used as a power source for industrial machines, such as those used in the mining, manufacturing, gas, and oil industries, as well as for back-up power generation in utility or commercial applications. Typical gas turbine engines may use a compressor to provide compressed air to a combustion section. In some turbine engines, combustion sections may include a plurality of combustors (i.e., “can combustors”) arranged annularly about a central shaft of the engine, each combustor having at least one fuel injector. Alternatively, a combustion section may include an annular combustor having a plurality of injectors disposed about an annular dome of the combustor. Compressed air may be mixed with fuel from the fuel injectors in the combustor and may be ignited by conventional means to generate combustion gases. The combustion gases may be discharged from the combustor into a turbine, which may extract energy from the gases to power various components of the engine and/or machine.
During operation, temperatures within the combustor may increase due to the exothermic combustion of the fuel/air mixture. The highest temperatures may be experienced by components located proximate the fuel injector. Accordingly, attempts have been made at providing cooling, coatings, and/or heat shields in the combustor liner for protecting combustor components from the thermal effects of combustion. Combustor components have also been cooled through impingement cooling methods wherein jets of cooling air are directed onto hot components of the combustor, or through film cooling.
For example, U.S. Pat. No. 5,490,389 to Harrison et al. (“the '389 patent”) describes a combustor having a fuel injector disposed in the center of a heat shield mounted to a bulkhead or dome of the combustor. The bulkhead has a plurality of holes for providing a flow of air between the bulkhead and the heat shield, which creates an outwardly circulating flow of air. The heat shield has a plurality of angled cooling holes for directing some of the cooling air through the heat shield, and outward, across its downstream face in order to film cool the heat shield. The heat shield is also cooled by a plurality of pedestals mounted to its upstream face.
Although the '389 patent provides for some cooling of the heat shield, and creates an outwardly circulating flow of air, its ability to provide sufficient cooling with reduced emissions may be limited. In particular, the outward flow between the bulkhead and heat shield may be insufficient. Moreover, the holes in the heat shield may result in flame extinction and increased emissions, especially in a lean pre-mix system. Finally, the heat shield of the '389 patent may be expensive and difficult to manufacture, due to the numerous pedestals and holes.
In another example, U.S. Pat. No. 6,497,105 to Stastny (“the '105 patent”) describes a combustor having a heat shield mounted to a bulkhead or dome of the combustor. Cooling air is directed from an annular gap around the fuel injector to the gap between the heat shield and the bulkhead. The heat shield has a plurality of holes for directing pressurized cooling air through the shield into the combustor chamber, in order to cool the bulkhead and heat shield. The heat shield also has a plurality of pins and inner and outer ridges extending outwardly away from the shield plate for increasing air contacting surfaces and forming air channels, respectively.
Although the '105 patent provides for some cooling of the heat shield, its ability to provide sufficient cooling with reduced emissions may be limited. Specifically, because cooling air is not directed from the periphery of the heat shield, and because the holes may allow cooling air to directly enter the combustion chamber, flame extinction may occur. Also, the numerous pins, ridges, and holes of the heat shield may require expensive and time consuming manufacturing techniques.